Reading The Road: How Will Driverless Cars Talk To Pedestrians?

No matter what vehicle we might be in, once we enter the road network, we start a constant information exchange with our fellow road-users. Signals, brake lights and road position give important clues to those around us on what we’re likely to do next. But it’s the more subtle human-to-human interactions that are particularly important for cyclists and pedestrians – a wave of a hand, or direct eye contact with a driver, can offer a sense of road safety that technology simply can’t. So, in a future filled with free-flowing, non-traffic-jam-inducing, driverless cars, will we be able to safely cross the road?

In technology terms, there’s no reason why not. OK yes, there’s a limit to how good a vehicle’s cameras can be – changing weather or a busy pavement can make it difficult for human drivers to spot crossing pedestrians. For an autonomous vehicle that relies on computers – even clever ones – it’s a much greater task. And then there’s the infrastructure. Even if driverless vehicles won’t necessarily need the red-amber-green signals that manage traffic today (as I described in a previous post), cyclists will, and our roads will still need to include dedicated crossing points for pedestrians. What happens at that crossing point is less clear though, and it leads onto the question of how manufacturers can build public trust in these vehicles.

Uber 'self-driving' cars are currently being tested in San Franscisco and Pittsburgh (Photo by Jeff Swensen/Getty Images)

Take the recent launch of Uber’s "self-driving" service, for example. Video footage has shown their cars running red lights, and witnesses (including Brian Wiedenmeier from the SF Bicycle Coalition) have reported them cutting across cycle lanes – executing the so-called "right-hook turn" that has previously been linked to the deaths of numerous cyclists. Not a good start. Uber also came to blows with the California DMV because they lacked the permits required to undertake these tests on public roads. Their cars are likely to return to testing in the coming weeks, but the bad press – and negative feeling amongst fellow road-users – doesn’t look like it’ll disappear anytime soon.

In 2016, Prof Natasha Merat from the University of Leeds surveyed 644 cyclists and pedestrians of all ages, in order to identify what concerned them most about interacting with driverless cars. As reported in the Guardian, the biggest request was for a clear, unambiguous way to signal to the road-user that they had been "seen" by the car’s sensors – a gesture that gives them the confidence to know what the autonomous car is about to do. So what form could this sort of interaction take?

In 2015, Nissan unveiled their “intention indicator” concept, which would use flashing lights and text projected on the windscreen to communicate with humans outside the vehicle. A 2015 patent from Google shows that they’re also considering text-based displays, as well as dedicated speakers to emit audible alerts. So, there’s no shortage of ideas, but as far as I could find, few have actually been implemented and tested by manufacturers. The team at the Humans and Autonomy Lab at Duke University are a different story, though. They recently published a paper (due to be presented next week at the Transportation Research Board) which evaluated a number of display-based options for vehicle-to-pedestrian communication.

Duke University are trying to understand how pedestrains might interact with driverless cars (Photo by Miles Aubert/Duke Robotics)

Their tests relied on a van, with a LCD display mounted on its grill, to represent an autonomous vehicle. It drove down a test track, and presented information to pedestrians crossing either at a marked crosswalk, or at an unmarked location. Now, as I mentioned earlier, there are a number of manufacturers looking at using a display, but in promotional images, it looks rather sexy – small, subtle text, running in an unobtrusive band along the bottom of the windscreen. The Duke paper suggests that this won’t work in practice though, thanks to U.S. standards for pedestrian signals, called the Manual on Uniform Traffic Control Devices. This document states that road-signage symbols should be at least 23 cm tall, if they need to be understood from 30 m away. For a display on a moving vehicle, that size would need to increase – to around 36 cm, according to this study.

With that in mind, the researchers, led by Prof Mary Cummings, displayed either the recognized symbols for “Walk” and “Don’t Walk” or speed advisory numbers (e.g. “25 mph”), in order to evaluate which made pedestrians feel safest when crossing. The results were surprising: there were no significant differences between the two display options, and both were only as effective as having no display at all. In fact, only 12% of the participants said that the display influenced their decision to cross, whether they were at a marked crosswalk or jaywalking. Despite the results, nearly half of the participants agreed that having “displays like the ones used in the experiment would be helpful when autonomous vehicles become available.”

So, maybe this study says more about human behavior than it does about driverless cars. Regardless, as manufacturers wrestle with incorporating a technology that’s very much “yes or no” into a world of “maybe,” it’s vital that the needs of all road-users are taken into account. Whatever vehicle-to-pedestrian option becomes the standard, it’ll need to be instantly recognizable to anyone, regardless of where they’re from, their physical ability, or who built the car that’s heading toward them.

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